1 nm Thick Functional Carbon Nanomembrane (CNM): New ...
Transcript of 1 nm Thick Functional Carbon Nanomembrane (CNM): New ...
1 nm Thick Functional Carbon
Nanomembrane (CNM) New Opportunities
for Nanotechnology
Min Ai and Armin Glzhuser
Physics of Supramolecular Systems and Surfaces University of BielefeldUniversitatsstraszlige 25 33615 Bielefeld Germany
E-MailE-Mail aguni-bielefeldde
Received 4th July 2013 Published 13th December 2013
Abstract
One nanometer thick mechanically stable carbon nanomembranes
(CNMs) are made by electron induced cross-linking of surface bound
self-assembled monolayers (SAMs) The cross-linked SAMs are then
released from the surface and can be placed onto solid materials or
spanned over holes as free-standing membranes Annealing at ~1000K
transforms CNMs into graphene or graphenoids accompanied by a
continuous change of mechanical stiffness and electrical resistance
from insulating to conducting which allows the tailoring of the CNMrsquos
electrical and mechanical properties Recently Janus membranes i e
CNMs functionalized by coupling different molecules to their top and
bottom surfaces were built Janus membranes have been built with
functional polymers proteins and dyes which demonstrates that Janus
CNMs can act as platforms for two-dimensional chemistry By com-
bining different types of CNMs hybrid nanolayers and biomimetic
membranes can be built
Introduction
Thin films are broadly and successfully integrated in many commercial products They are
used for surface lubrication corrosion inhibition or to avoid bio-fouling other applications
include barrier and separation membranes light-emitting diodes photo detectors transistors
memory and bio (chemical) sensors [1] Most of these applications require a high thermal
167
httpwwwbeilstein-institutdeBozen2012ProceedingsGolzhauserGolzhauserpdf
Beilstein Bozen Symposium on Molecular Engineering and Control
May 14th ndash 18th 2012 Prien (Chiemsee) Germany
and mechanical stability while it is desirable that the films are as thin as possible Commer-
cially available thin films have thicknesses ranging from a few 100 nm to several mm
However due to their extremely large surface-to-volume ratio we expect that films with a
much smaller thickness (lt 100 nm) would be even more attractive for fundamental studies as
well as for industry Several ways to fabricate ultrathin films are currently explored layer-
by-layer (LbL) films of polyelectrolytes [2] spin-coating [3] interfacial polymeric mem-
branes [4] Langmuir-Blodgett [5] chemical vapor deposition as well as the exfoliation of
bulk materials into graphene [6 7] or transition metal dichalcogenides [8]
Other fabrication strategies are based on molecular self-assembly Self-assembled mono-
layers (SAMs) of amphiphilic molecules have the thickness of a single molecule ~1 nm
When aromatic SAMs are exposed to radiation they form cross-links between neighboring
molecules The resulting molecular network can be released from the surface as a free-
standing two-dimensional carbon nanomembrane (CNM) As amphiphilic molecules have
two distinct functional groups the resulting CNM also has two sides of distinct chemical
functionality and both sides can be chemically modified with dissimilar molecules resulting
in lsquolsquoJanus membranesrsquorsquo CNMs can also be converted into graphene by annealing in ultra-
high vacuum This diverse chemistry and broad functionality open new pathways for funda-
mental and applied research
This article summarizes recent progress in the fabrication characterization and application of
CNMs The main text is organized into two sections the first emphasizing on the synthesis
and preparation strategies that have been developed for achieving the 1 nm thick CNMs and
the analysis techniques that were used to characterize their physical and chemical properties
The second part is to discuss prospects of their applications in nanotechnology e g being
potentially integrated in lab-on-a-chip technology electronics and micro-nano-electro me-
chanical systems
Fabrication and characterization of CNMs
1 Fabrication
The first step in the making of CNMs is the preparation of a well-defined self-assembled
monolayer of aromatic amphiphilic molecules on a surface A SAM can be obtained by
adsorption from solution or by vapor phase deposition in vacuum Depending on types of
molecules and surfaces SAMs with different degrees of order form These SAMs are then
irradiated by electrons [9] or UV-light [10] which starts a dehydrogenation and recombina-
tion mechanism that leads to a two-dimensional cross-linking of molecules into a CNM [11]
After cross-linking CNM is detached from the original surface and exhibits a free-standing
ultra-thin film with a thickness of the length of the SAM molecule (about 1 nm for a
biphenyl molecule) [12] Examples are presented in Table 1
168
Ai M and Golzhauser A
Table 1 CNM formation from molecules on appropriate substrates by electron beam
and agents
SAM Anchor moiety Substrate Removing agent
Biphenylthiol orNitrobiphenylthiol
-S Au I2
Biphenylthiol orNitrobiphenylthiol
-S Cu Ammonium persulfate + water
Biphenylcarboxylic acid -COOH Ag2O Ammonia solution (aq)
Biphenylhydroxamic acid -CO-NH-OH FeTi AcidE-beam
Biphenylsilane orHydroxybiphenyl
-OH or ndashSiR3 Si HF or KOH
Biphenylcarbonxylic acid orNitrobiphenylcarboxylic acid
-COOH ITO Acid
2 Characterizing 1-nm-thick CNMs
Several analytical techniques for characterizing CNMs have been exploited Among them
optical microscopy scanning electron microscopy (SEM) atomic force microscopy (AFM)
helium ion microscopy (HIM) and transmission electron microscopy (TEM) provided an
opportunity to study the morphology optical and mechanical properties of CNM [13] To
elucidate the structure and composition of CNMs spectroscopic techniques such as infrared
reflection absorption spectroscopy (IRRAS) X-ray and UV photoelectron spectroscopy
(XPS UPS) and Raman spectroscopy were utilized [9]
21 Imaging CNM
A 1 nm thick CNM is transparent in visible light However when it is placed onto a ~300
nm SiO2 layer on a Si substrate it can be detected with the naked eye cf Fig 1 [13] In Fig
1B ribbons of CNMs on SiO2Si appear dark and blue shifted with respect to the substrate
color in optical micrographs and two or three layers stacked on each other yield a higher
contrast and blue shift because of interference contrast which results from light passing
through layered structures with different dielectric properties here the CNMs and the
supporting SiO2 on Si Since interference contrast results in a clearly visible color change
of the areas covered by CNMs and other thin nanofilms it becomes a simple way of imaging
such thin films
CNMs were also imaged by helium ion microscopy (HIM) After being transferred onto
metal grids they became free-standing suspended on the holey support Fig 1C displays a
free-standing CNM that spans over ~40 mm wide openings in metal grids where finer
structures wrinkles and defects are visualized Scanning electron microscopy (SEM) can
also be utilized to image CNMs by transferring them onto a perforated (2 mm holes) carbon
169
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
foil and directly imaging them by SEM (Fig 1C (right)) If the same sample is imaged by
HIM (Fig 1C (left)) the helium ion image reveals a much higher contrast than the SEM
image
Figure 1 (A) Photograph of a cm2-sized CNM (larger than one cent euro coin) on a
SiO2Si wafer The CNM is visible due to Raleighrsquos interference contrast (B) Optical
micrograph of ~10 mm width CNM ribbons on a SiO2Si wafer i) A single layer ii)
Two layers transferred at a ~90 angle iii) Three layers at an angle of ~60 Each layer
gives rise to a further blue shift (C) HIM images of a CNM transferred onto a
hexagonal pore (~40 mm in diameter) (D) Comparison of HIM and SEM images of
a 1 nm thick CNM on a quantifoil TEM support
22 Spectroscopic observation of the cross-linking
X-ray photoelectron spectroscopy was utilized to investigate the composition of SAMs as
well as radiation induced changes Figure 2 displays C1 s N1 s S2 p and O1 s spectra of
4-nitro-11rsquo-biphenyl-4-thiol on a gold substrate as recorded before and after irradiation by
VUV under ultrahigh vacuum (UHV) conditions The shift of the N1 s binding energy (BE)
from 4056 eV to 3993 eV results from the chemical conversion of nitro groups to amino
groups after irradiation with VUV Characteristic changes also occur in the S2 p and O1 s
signals A broadening of the S2 p spectrum towards higher binding energies is attributed to a
partial oxidation of the thiol species at the SAMgold interface The O1 s signal is signifi-
cantly reduced after irradiation with VUV which is explained by a loss of oxygen from nitro
groups when they convert into amino groups The thickness of SAM or CNM on the gold
substrate can be determined from the attenuation of the Au4f7 2 signal by the monolayer
The film thicknesses of SAMs (125 plusmn 08 nm) and CNMs (121 plusmn 09 nm) are obtained from
these spectra [10]
170
Ai M and Golzhauser A
Figure 2 XP spectra of 4rsquo-nitro-11rsquo-biphenyl-4-thiol on gold before and after VUV
(He I 212 eV) irradiation The generation of amino groups can be clearly recognized
from the corresponding chemical shift from 4055 eV to 3992 eV [10]
23 Thermal stability
Thermal stability is important for the integration of CNMs in electronic devices Turchanin
El-Desawy and Golzhauser [14] found that cross-linked SAMs are thermally stable up to
1000 K In their experiment pristine SAMs and CNMs were heated on Au substrates in
steps of 20 ndash 50 K from room temperature to 1000 K and then studied by XPS [14] In
Fig 3A after heating to 470 K the C1 s signal of the pristine SAMs showed only 10 of its
initial intensity indicating SAM decomposition or desorption but the C1 s signal of CNMs
appears at 90 intensity Figure 3B shows a plot of the intensity of the C1 s signal of
pristine and electron irradiated BPT as a function of temperature and dose The pristine
SAMs desorbed at about 400 K and the XPS intensity of CNM after irradiation at
25 mCcm2 electron dosage lead to 50 loss Upon annealing to 1000 K 80 of the
CNM XPS intensity was still observed after 45 mCcm2 electron dosage irradiation Lower
electron dosage leads to the partially cross-linked SAM
171
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 3 (A) XPS spectra of the C1 s and S2 p signals (a) Pristine biphenythiol
SAM (BPT) at room temperature (b) Cross-linked BPT (45 mCcm2) at RT (c)
Pristine BPT after annealing at 470 K (d) Cross-linked BPT after annealing at
470K (B) Temperature dependence of the C1 s signal of BPT as a function of
irradiation dose [14]
24 Electrical resistance
The performance of CNMs in electronic devices of course depends on their electrical
conductivity The sheet resistance of CNMs that have been annealed at temperatures be-
tween 800 K and 1200 K was determined by a two-point measurement in UHV scanning
tunneling microscopy (STM) and by four-point in ambient conditions CNMs suspended on
a gold grid were directly contacted by a STM tip in UHV The resistance was determined
from the current between the tip and the surrounding frame (Fig 4A) CNMs were also
transferred onto non-conductive silicon oxide and were then measured with four-probes
(Fig 4bB) [12] Figure 4C shows the sheet resistivity as a function of the annealing tem-
perature After annealing CNMs at ~800 K we find a sheet resistivity of ~10-8 kWsq-1 upon
rising the annealing temperature to ~1200 K this comes down to ~100 kWsq-1 The reason
for this unusual behavior is that upon annealing CNMs transform into graphene and thus
become conductive as will be described in more detail in section 27
172
Ai M and Golzhauser A
Figure 4 The resistivity of CNMs was determined by a two-point (STM) in UHV (A)
and four-point in ambient conditions (B) (C) The sheet resistivity corresponds to 10-8
kWsq-1 after annealing at 800 K Upon annealing to temperatures between 800 and
1200 K the currentvoltage curves are linear Increasing the annealing temperature to
1200 K the sheet resistivity drops to 100 kWsq-1 [12]
Multilayers of CNMs after annealing show more conductivity than a single layer of CNMs
as in Fig 5 [15] Upon annealing to 1100 K the sheet resistivity dropped further to 108
303 and 372 kWs q-1 for five four and three layers respectively This tunable electrical
conductivity of CNMs from an insulator to a conductor by annealing temperatures or
amounts of layers will be of value for CNMs to be utilized in micro- or nano-electronics
Figure 5 (A) RT sheet resistivity
of BPT multilayers as a function
of annealing temperature The er-
ror bars represent the standard de-
viation of measurements at differ-
ent spots on the samples (B) RT
linear currentndashvoltage curves for
2- 3- 4- and 5-layer samples
after annealing at 1100 K [15]
173
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
and mechanical stability while it is desirable that the films are as thin as possible Commer-
cially available thin films have thicknesses ranging from a few 100 nm to several mm
However due to their extremely large surface-to-volume ratio we expect that films with a
much smaller thickness (lt 100 nm) would be even more attractive for fundamental studies as
well as for industry Several ways to fabricate ultrathin films are currently explored layer-
by-layer (LbL) films of polyelectrolytes [2] spin-coating [3] interfacial polymeric mem-
branes [4] Langmuir-Blodgett [5] chemical vapor deposition as well as the exfoliation of
bulk materials into graphene [6 7] or transition metal dichalcogenides [8]
Other fabrication strategies are based on molecular self-assembly Self-assembled mono-
layers (SAMs) of amphiphilic molecules have the thickness of a single molecule ~1 nm
When aromatic SAMs are exposed to radiation they form cross-links between neighboring
molecules The resulting molecular network can be released from the surface as a free-
standing two-dimensional carbon nanomembrane (CNM) As amphiphilic molecules have
two distinct functional groups the resulting CNM also has two sides of distinct chemical
functionality and both sides can be chemically modified with dissimilar molecules resulting
in lsquolsquoJanus membranesrsquorsquo CNMs can also be converted into graphene by annealing in ultra-
high vacuum This diverse chemistry and broad functionality open new pathways for funda-
mental and applied research
This article summarizes recent progress in the fabrication characterization and application of
CNMs The main text is organized into two sections the first emphasizing on the synthesis
and preparation strategies that have been developed for achieving the 1 nm thick CNMs and
the analysis techniques that were used to characterize their physical and chemical properties
The second part is to discuss prospects of their applications in nanotechnology e g being
potentially integrated in lab-on-a-chip technology electronics and micro-nano-electro me-
chanical systems
Fabrication and characterization of CNMs
1 Fabrication
The first step in the making of CNMs is the preparation of a well-defined self-assembled
monolayer of aromatic amphiphilic molecules on a surface A SAM can be obtained by
adsorption from solution or by vapor phase deposition in vacuum Depending on types of
molecules and surfaces SAMs with different degrees of order form These SAMs are then
irradiated by electrons [9] or UV-light [10] which starts a dehydrogenation and recombina-
tion mechanism that leads to a two-dimensional cross-linking of molecules into a CNM [11]
After cross-linking CNM is detached from the original surface and exhibits a free-standing
ultra-thin film with a thickness of the length of the SAM molecule (about 1 nm for a
biphenyl molecule) [12] Examples are presented in Table 1
168
Ai M and Golzhauser A
Table 1 CNM formation from molecules on appropriate substrates by electron beam
and agents
SAM Anchor moiety Substrate Removing agent
Biphenylthiol orNitrobiphenylthiol
-S Au I2
Biphenylthiol orNitrobiphenylthiol
-S Cu Ammonium persulfate + water
Biphenylcarboxylic acid -COOH Ag2O Ammonia solution (aq)
Biphenylhydroxamic acid -CO-NH-OH FeTi AcidE-beam
Biphenylsilane orHydroxybiphenyl
-OH or ndashSiR3 Si HF or KOH
Biphenylcarbonxylic acid orNitrobiphenylcarboxylic acid
-COOH ITO Acid
2 Characterizing 1-nm-thick CNMs
Several analytical techniques for characterizing CNMs have been exploited Among them
optical microscopy scanning electron microscopy (SEM) atomic force microscopy (AFM)
helium ion microscopy (HIM) and transmission electron microscopy (TEM) provided an
opportunity to study the morphology optical and mechanical properties of CNM [13] To
elucidate the structure and composition of CNMs spectroscopic techniques such as infrared
reflection absorption spectroscopy (IRRAS) X-ray and UV photoelectron spectroscopy
(XPS UPS) and Raman spectroscopy were utilized [9]
21 Imaging CNM
A 1 nm thick CNM is transparent in visible light However when it is placed onto a ~300
nm SiO2 layer on a Si substrate it can be detected with the naked eye cf Fig 1 [13] In Fig
1B ribbons of CNMs on SiO2Si appear dark and blue shifted with respect to the substrate
color in optical micrographs and two or three layers stacked on each other yield a higher
contrast and blue shift because of interference contrast which results from light passing
through layered structures with different dielectric properties here the CNMs and the
supporting SiO2 on Si Since interference contrast results in a clearly visible color change
of the areas covered by CNMs and other thin nanofilms it becomes a simple way of imaging
such thin films
CNMs were also imaged by helium ion microscopy (HIM) After being transferred onto
metal grids they became free-standing suspended on the holey support Fig 1C displays a
free-standing CNM that spans over ~40 mm wide openings in metal grids where finer
structures wrinkles and defects are visualized Scanning electron microscopy (SEM) can
also be utilized to image CNMs by transferring them onto a perforated (2 mm holes) carbon
169
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
foil and directly imaging them by SEM (Fig 1C (right)) If the same sample is imaged by
HIM (Fig 1C (left)) the helium ion image reveals a much higher contrast than the SEM
image
Figure 1 (A) Photograph of a cm2-sized CNM (larger than one cent euro coin) on a
SiO2Si wafer The CNM is visible due to Raleighrsquos interference contrast (B) Optical
micrograph of ~10 mm width CNM ribbons on a SiO2Si wafer i) A single layer ii)
Two layers transferred at a ~90 angle iii) Three layers at an angle of ~60 Each layer
gives rise to a further blue shift (C) HIM images of a CNM transferred onto a
hexagonal pore (~40 mm in diameter) (D) Comparison of HIM and SEM images of
a 1 nm thick CNM on a quantifoil TEM support
22 Spectroscopic observation of the cross-linking
X-ray photoelectron spectroscopy was utilized to investigate the composition of SAMs as
well as radiation induced changes Figure 2 displays C1 s N1 s S2 p and O1 s spectra of
4-nitro-11rsquo-biphenyl-4-thiol on a gold substrate as recorded before and after irradiation by
VUV under ultrahigh vacuum (UHV) conditions The shift of the N1 s binding energy (BE)
from 4056 eV to 3993 eV results from the chemical conversion of nitro groups to amino
groups after irradiation with VUV Characteristic changes also occur in the S2 p and O1 s
signals A broadening of the S2 p spectrum towards higher binding energies is attributed to a
partial oxidation of the thiol species at the SAMgold interface The O1 s signal is signifi-
cantly reduced after irradiation with VUV which is explained by a loss of oxygen from nitro
groups when they convert into amino groups The thickness of SAM or CNM on the gold
substrate can be determined from the attenuation of the Au4f7 2 signal by the monolayer
The film thicknesses of SAMs (125 plusmn 08 nm) and CNMs (121 plusmn 09 nm) are obtained from
these spectra [10]
170
Ai M and Golzhauser A
Figure 2 XP spectra of 4rsquo-nitro-11rsquo-biphenyl-4-thiol on gold before and after VUV
(He I 212 eV) irradiation The generation of amino groups can be clearly recognized
from the corresponding chemical shift from 4055 eV to 3992 eV [10]
23 Thermal stability
Thermal stability is important for the integration of CNMs in electronic devices Turchanin
El-Desawy and Golzhauser [14] found that cross-linked SAMs are thermally stable up to
1000 K In their experiment pristine SAMs and CNMs were heated on Au substrates in
steps of 20 ndash 50 K from room temperature to 1000 K and then studied by XPS [14] In
Fig 3A after heating to 470 K the C1 s signal of the pristine SAMs showed only 10 of its
initial intensity indicating SAM decomposition or desorption but the C1 s signal of CNMs
appears at 90 intensity Figure 3B shows a plot of the intensity of the C1 s signal of
pristine and electron irradiated BPT as a function of temperature and dose The pristine
SAMs desorbed at about 400 K and the XPS intensity of CNM after irradiation at
25 mCcm2 electron dosage lead to 50 loss Upon annealing to 1000 K 80 of the
CNM XPS intensity was still observed after 45 mCcm2 electron dosage irradiation Lower
electron dosage leads to the partially cross-linked SAM
171
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 3 (A) XPS spectra of the C1 s and S2 p signals (a) Pristine biphenythiol
SAM (BPT) at room temperature (b) Cross-linked BPT (45 mCcm2) at RT (c)
Pristine BPT after annealing at 470 K (d) Cross-linked BPT after annealing at
470K (B) Temperature dependence of the C1 s signal of BPT as a function of
irradiation dose [14]
24 Electrical resistance
The performance of CNMs in electronic devices of course depends on their electrical
conductivity The sheet resistance of CNMs that have been annealed at temperatures be-
tween 800 K and 1200 K was determined by a two-point measurement in UHV scanning
tunneling microscopy (STM) and by four-point in ambient conditions CNMs suspended on
a gold grid were directly contacted by a STM tip in UHV The resistance was determined
from the current between the tip and the surrounding frame (Fig 4A) CNMs were also
transferred onto non-conductive silicon oxide and were then measured with four-probes
(Fig 4bB) [12] Figure 4C shows the sheet resistivity as a function of the annealing tem-
perature After annealing CNMs at ~800 K we find a sheet resistivity of ~10-8 kWsq-1 upon
rising the annealing temperature to ~1200 K this comes down to ~100 kWsq-1 The reason
for this unusual behavior is that upon annealing CNMs transform into graphene and thus
become conductive as will be described in more detail in section 27
172
Ai M and Golzhauser A
Figure 4 The resistivity of CNMs was determined by a two-point (STM) in UHV (A)
and four-point in ambient conditions (B) (C) The sheet resistivity corresponds to 10-8
kWsq-1 after annealing at 800 K Upon annealing to temperatures between 800 and
1200 K the currentvoltage curves are linear Increasing the annealing temperature to
1200 K the sheet resistivity drops to 100 kWsq-1 [12]
Multilayers of CNMs after annealing show more conductivity than a single layer of CNMs
as in Fig 5 [15] Upon annealing to 1100 K the sheet resistivity dropped further to 108
303 and 372 kWs q-1 for five four and three layers respectively This tunable electrical
conductivity of CNMs from an insulator to a conductor by annealing temperatures or
amounts of layers will be of value for CNMs to be utilized in micro- or nano-electronics
Figure 5 (A) RT sheet resistivity
of BPT multilayers as a function
of annealing temperature The er-
ror bars represent the standard de-
viation of measurements at differ-
ent spots on the samples (B) RT
linear currentndashvoltage curves for
2- 3- 4- and 5-layer samples
after annealing at 1100 K [15]
173
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
Table 1 CNM formation from molecules on appropriate substrates by electron beam
and agents
SAM Anchor moiety Substrate Removing agent
Biphenylthiol orNitrobiphenylthiol
-S Au I2
Biphenylthiol orNitrobiphenylthiol
-S Cu Ammonium persulfate + water
Biphenylcarboxylic acid -COOH Ag2O Ammonia solution (aq)
Biphenylhydroxamic acid -CO-NH-OH FeTi AcidE-beam
Biphenylsilane orHydroxybiphenyl
-OH or ndashSiR3 Si HF or KOH
Biphenylcarbonxylic acid orNitrobiphenylcarboxylic acid
-COOH ITO Acid
2 Characterizing 1-nm-thick CNMs
Several analytical techniques for characterizing CNMs have been exploited Among them
optical microscopy scanning electron microscopy (SEM) atomic force microscopy (AFM)
helium ion microscopy (HIM) and transmission electron microscopy (TEM) provided an
opportunity to study the morphology optical and mechanical properties of CNM [13] To
elucidate the structure and composition of CNMs spectroscopic techniques such as infrared
reflection absorption spectroscopy (IRRAS) X-ray and UV photoelectron spectroscopy
(XPS UPS) and Raman spectroscopy were utilized [9]
21 Imaging CNM
A 1 nm thick CNM is transparent in visible light However when it is placed onto a ~300
nm SiO2 layer on a Si substrate it can be detected with the naked eye cf Fig 1 [13] In Fig
1B ribbons of CNMs on SiO2Si appear dark and blue shifted with respect to the substrate
color in optical micrographs and two or three layers stacked on each other yield a higher
contrast and blue shift because of interference contrast which results from light passing
through layered structures with different dielectric properties here the CNMs and the
supporting SiO2 on Si Since interference contrast results in a clearly visible color change
of the areas covered by CNMs and other thin nanofilms it becomes a simple way of imaging
such thin films
CNMs were also imaged by helium ion microscopy (HIM) After being transferred onto
metal grids they became free-standing suspended on the holey support Fig 1C displays a
free-standing CNM that spans over ~40 mm wide openings in metal grids where finer
structures wrinkles and defects are visualized Scanning electron microscopy (SEM) can
also be utilized to image CNMs by transferring them onto a perforated (2 mm holes) carbon
169
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
foil and directly imaging them by SEM (Fig 1C (right)) If the same sample is imaged by
HIM (Fig 1C (left)) the helium ion image reveals a much higher contrast than the SEM
image
Figure 1 (A) Photograph of a cm2-sized CNM (larger than one cent euro coin) on a
SiO2Si wafer The CNM is visible due to Raleighrsquos interference contrast (B) Optical
micrograph of ~10 mm width CNM ribbons on a SiO2Si wafer i) A single layer ii)
Two layers transferred at a ~90 angle iii) Three layers at an angle of ~60 Each layer
gives rise to a further blue shift (C) HIM images of a CNM transferred onto a
hexagonal pore (~40 mm in diameter) (D) Comparison of HIM and SEM images of
a 1 nm thick CNM on a quantifoil TEM support
22 Spectroscopic observation of the cross-linking
X-ray photoelectron spectroscopy was utilized to investigate the composition of SAMs as
well as radiation induced changes Figure 2 displays C1 s N1 s S2 p and O1 s spectra of
4-nitro-11rsquo-biphenyl-4-thiol on a gold substrate as recorded before and after irradiation by
VUV under ultrahigh vacuum (UHV) conditions The shift of the N1 s binding energy (BE)
from 4056 eV to 3993 eV results from the chemical conversion of nitro groups to amino
groups after irradiation with VUV Characteristic changes also occur in the S2 p and O1 s
signals A broadening of the S2 p spectrum towards higher binding energies is attributed to a
partial oxidation of the thiol species at the SAMgold interface The O1 s signal is signifi-
cantly reduced after irradiation with VUV which is explained by a loss of oxygen from nitro
groups when they convert into amino groups The thickness of SAM or CNM on the gold
substrate can be determined from the attenuation of the Au4f7 2 signal by the monolayer
The film thicknesses of SAMs (125 plusmn 08 nm) and CNMs (121 plusmn 09 nm) are obtained from
these spectra [10]
170
Ai M and Golzhauser A
Figure 2 XP spectra of 4rsquo-nitro-11rsquo-biphenyl-4-thiol on gold before and after VUV
(He I 212 eV) irradiation The generation of amino groups can be clearly recognized
from the corresponding chemical shift from 4055 eV to 3992 eV [10]
23 Thermal stability
Thermal stability is important for the integration of CNMs in electronic devices Turchanin
El-Desawy and Golzhauser [14] found that cross-linked SAMs are thermally stable up to
1000 K In their experiment pristine SAMs and CNMs were heated on Au substrates in
steps of 20 ndash 50 K from room temperature to 1000 K and then studied by XPS [14] In
Fig 3A after heating to 470 K the C1 s signal of the pristine SAMs showed only 10 of its
initial intensity indicating SAM decomposition or desorption but the C1 s signal of CNMs
appears at 90 intensity Figure 3B shows a plot of the intensity of the C1 s signal of
pristine and electron irradiated BPT as a function of temperature and dose The pristine
SAMs desorbed at about 400 K and the XPS intensity of CNM after irradiation at
25 mCcm2 electron dosage lead to 50 loss Upon annealing to 1000 K 80 of the
CNM XPS intensity was still observed after 45 mCcm2 electron dosage irradiation Lower
electron dosage leads to the partially cross-linked SAM
171
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 3 (A) XPS spectra of the C1 s and S2 p signals (a) Pristine biphenythiol
SAM (BPT) at room temperature (b) Cross-linked BPT (45 mCcm2) at RT (c)
Pristine BPT after annealing at 470 K (d) Cross-linked BPT after annealing at
470K (B) Temperature dependence of the C1 s signal of BPT as a function of
irradiation dose [14]
24 Electrical resistance
The performance of CNMs in electronic devices of course depends on their electrical
conductivity The sheet resistance of CNMs that have been annealed at temperatures be-
tween 800 K and 1200 K was determined by a two-point measurement in UHV scanning
tunneling microscopy (STM) and by four-point in ambient conditions CNMs suspended on
a gold grid were directly contacted by a STM tip in UHV The resistance was determined
from the current between the tip and the surrounding frame (Fig 4A) CNMs were also
transferred onto non-conductive silicon oxide and were then measured with four-probes
(Fig 4bB) [12] Figure 4C shows the sheet resistivity as a function of the annealing tem-
perature After annealing CNMs at ~800 K we find a sheet resistivity of ~10-8 kWsq-1 upon
rising the annealing temperature to ~1200 K this comes down to ~100 kWsq-1 The reason
for this unusual behavior is that upon annealing CNMs transform into graphene and thus
become conductive as will be described in more detail in section 27
172
Ai M and Golzhauser A
Figure 4 The resistivity of CNMs was determined by a two-point (STM) in UHV (A)
and four-point in ambient conditions (B) (C) The sheet resistivity corresponds to 10-8
kWsq-1 after annealing at 800 K Upon annealing to temperatures between 800 and
1200 K the currentvoltage curves are linear Increasing the annealing temperature to
1200 K the sheet resistivity drops to 100 kWsq-1 [12]
Multilayers of CNMs after annealing show more conductivity than a single layer of CNMs
as in Fig 5 [15] Upon annealing to 1100 K the sheet resistivity dropped further to 108
303 and 372 kWs q-1 for five four and three layers respectively This tunable electrical
conductivity of CNMs from an insulator to a conductor by annealing temperatures or
amounts of layers will be of value for CNMs to be utilized in micro- or nano-electronics
Figure 5 (A) RT sheet resistivity
of BPT multilayers as a function
of annealing temperature The er-
ror bars represent the standard de-
viation of measurements at differ-
ent spots on the samples (B) RT
linear currentndashvoltage curves for
2- 3- 4- and 5-layer samples
after annealing at 1100 K [15]
173
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
foil and directly imaging them by SEM (Fig 1C (right)) If the same sample is imaged by
HIM (Fig 1C (left)) the helium ion image reveals a much higher contrast than the SEM
image
Figure 1 (A) Photograph of a cm2-sized CNM (larger than one cent euro coin) on a
SiO2Si wafer The CNM is visible due to Raleighrsquos interference contrast (B) Optical
micrograph of ~10 mm width CNM ribbons on a SiO2Si wafer i) A single layer ii)
Two layers transferred at a ~90 angle iii) Three layers at an angle of ~60 Each layer
gives rise to a further blue shift (C) HIM images of a CNM transferred onto a
hexagonal pore (~40 mm in diameter) (D) Comparison of HIM and SEM images of
a 1 nm thick CNM on a quantifoil TEM support
22 Spectroscopic observation of the cross-linking
X-ray photoelectron spectroscopy was utilized to investigate the composition of SAMs as
well as radiation induced changes Figure 2 displays C1 s N1 s S2 p and O1 s spectra of
4-nitro-11rsquo-biphenyl-4-thiol on a gold substrate as recorded before and after irradiation by
VUV under ultrahigh vacuum (UHV) conditions The shift of the N1 s binding energy (BE)
from 4056 eV to 3993 eV results from the chemical conversion of nitro groups to amino
groups after irradiation with VUV Characteristic changes also occur in the S2 p and O1 s
signals A broadening of the S2 p spectrum towards higher binding energies is attributed to a
partial oxidation of the thiol species at the SAMgold interface The O1 s signal is signifi-
cantly reduced after irradiation with VUV which is explained by a loss of oxygen from nitro
groups when they convert into amino groups The thickness of SAM or CNM on the gold
substrate can be determined from the attenuation of the Au4f7 2 signal by the monolayer
The film thicknesses of SAMs (125 plusmn 08 nm) and CNMs (121 plusmn 09 nm) are obtained from
these spectra [10]
170
Ai M and Golzhauser A
Figure 2 XP spectra of 4rsquo-nitro-11rsquo-biphenyl-4-thiol on gold before and after VUV
(He I 212 eV) irradiation The generation of amino groups can be clearly recognized
from the corresponding chemical shift from 4055 eV to 3992 eV [10]
23 Thermal stability
Thermal stability is important for the integration of CNMs in electronic devices Turchanin
El-Desawy and Golzhauser [14] found that cross-linked SAMs are thermally stable up to
1000 K In their experiment pristine SAMs and CNMs were heated on Au substrates in
steps of 20 ndash 50 K from room temperature to 1000 K and then studied by XPS [14] In
Fig 3A after heating to 470 K the C1 s signal of the pristine SAMs showed only 10 of its
initial intensity indicating SAM decomposition or desorption but the C1 s signal of CNMs
appears at 90 intensity Figure 3B shows a plot of the intensity of the C1 s signal of
pristine and electron irradiated BPT as a function of temperature and dose The pristine
SAMs desorbed at about 400 K and the XPS intensity of CNM after irradiation at
25 mCcm2 electron dosage lead to 50 loss Upon annealing to 1000 K 80 of the
CNM XPS intensity was still observed after 45 mCcm2 electron dosage irradiation Lower
electron dosage leads to the partially cross-linked SAM
171
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 3 (A) XPS spectra of the C1 s and S2 p signals (a) Pristine biphenythiol
SAM (BPT) at room temperature (b) Cross-linked BPT (45 mCcm2) at RT (c)
Pristine BPT after annealing at 470 K (d) Cross-linked BPT after annealing at
470K (B) Temperature dependence of the C1 s signal of BPT as a function of
irradiation dose [14]
24 Electrical resistance
The performance of CNMs in electronic devices of course depends on their electrical
conductivity The sheet resistance of CNMs that have been annealed at temperatures be-
tween 800 K and 1200 K was determined by a two-point measurement in UHV scanning
tunneling microscopy (STM) and by four-point in ambient conditions CNMs suspended on
a gold grid were directly contacted by a STM tip in UHV The resistance was determined
from the current between the tip and the surrounding frame (Fig 4A) CNMs were also
transferred onto non-conductive silicon oxide and were then measured with four-probes
(Fig 4bB) [12] Figure 4C shows the sheet resistivity as a function of the annealing tem-
perature After annealing CNMs at ~800 K we find a sheet resistivity of ~10-8 kWsq-1 upon
rising the annealing temperature to ~1200 K this comes down to ~100 kWsq-1 The reason
for this unusual behavior is that upon annealing CNMs transform into graphene and thus
become conductive as will be described in more detail in section 27
172
Ai M and Golzhauser A
Figure 4 The resistivity of CNMs was determined by a two-point (STM) in UHV (A)
and four-point in ambient conditions (B) (C) The sheet resistivity corresponds to 10-8
kWsq-1 after annealing at 800 K Upon annealing to temperatures between 800 and
1200 K the currentvoltage curves are linear Increasing the annealing temperature to
1200 K the sheet resistivity drops to 100 kWsq-1 [12]
Multilayers of CNMs after annealing show more conductivity than a single layer of CNMs
as in Fig 5 [15] Upon annealing to 1100 K the sheet resistivity dropped further to 108
303 and 372 kWs q-1 for five four and three layers respectively This tunable electrical
conductivity of CNMs from an insulator to a conductor by annealing temperatures or
amounts of layers will be of value for CNMs to be utilized in micro- or nano-electronics
Figure 5 (A) RT sheet resistivity
of BPT multilayers as a function
of annealing temperature The er-
ror bars represent the standard de-
viation of measurements at differ-
ent spots on the samples (B) RT
linear currentndashvoltage curves for
2- 3- 4- and 5-layer samples
after annealing at 1100 K [15]
173
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
Figure 2 XP spectra of 4rsquo-nitro-11rsquo-biphenyl-4-thiol on gold before and after VUV
(He I 212 eV) irradiation The generation of amino groups can be clearly recognized
from the corresponding chemical shift from 4055 eV to 3992 eV [10]
23 Thermal stability
Thermal stability is important for the integration of CNMs in electronic devices Turchanin
El-Desawy and Golzhauser [14] found that cross-linked SAMs are thermally stable up to
1000 K In their experiment pristine SAMs and CNMs were heated on Au substrates in
steps of 20 ndash 50 K from room temperature to 1000 K and then studied by XPS [14] In
Fig 3A after heating to 470 K the C1 s signal of the pristine SAMs showed only 10 of its
initial intensity indicating SAM decomposition or desorption but the C1 s signal of CNMs
appears at 90 intensity Figure 3B shows a plot of the intensity of the C1 s signal of
pristine and electron irradiated BPT as a function of temperature and dose The pristine
SAMs desorbed at about 400 K and the XPS intensity of CNM after irradiation at
25 mCcm2 electron dosage lead to 50 loss Upon annealing to 1000 K 80 of the
CNM XPS intensity was still observed after 45 mCcm2 electron dosage irradiation Lower
electron dosage leads to the partially cross-linked SAM
171
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 3 (A) XPS spectra of the C1 s and S2 p signals (a) Pristine biphenythiol
SAM (BPT) at room temperature (b) Cross-linked BPT (45 mCcm2) at RT (c)
Pristine BPT after annealing at 470 K (d) Cross-linked BPT after annealing at
470K (B) Temperature dependence of the C1 s signal of BPT as a function of
irradiation dose [14]
24 Electrical resistance
The performance of CNMs in electronic devices of course depends on their electrical
conductivity The sheet resistance of CNMs that have been annealed at temperatures be-
tween 800 K and 1200 K was determined by a two-point measurement in UHV scanning
tunneling microscopy (STM) and by four-point in ambient conditions CNMs suspended on
a gold grid were directly contacted by a STM tip in UHV The resistance was determined
from the current between the tip and the surrounding frame (Fig 4A) CNMs were also
transferred onto non-conductive silicon oxide and were then measured with four-probes
(Fig 4bB) [12] Figure 4C shows the sheet resistivity as a function of the annealing tem-
perature After annealing CNMs at ~800 K we find a sheet resistivity of ~10-8 kWsq-1 upon
rising the annealing temperature to ~1200 K this comes down to ~100 kWsq-1 The reason
for this unusual behavior is that upon annealing CNMs transform into graphene and thus
become conductive as will be described in more detail in section 27
172
Ai M and Golzhauser A
Figure 4 The resistivity of CNMs was determined by a two-point (STM) in UHV (A)
and four-point in ambient conditions (B) (C) The sheet resistivity corresponds to 10-8
kWsq-1 after annealing at 800 K Upon annealing to temperatures between 800 and
1200 K the currentvoltage curves are linear Increasing the annealing temperature to
1200 K the sheet resistivity drops to 100 kWsq-1 [12]
Multilayers of CNMs after annealing show more conductivity than a single layer of CNMs
as in Fig 5 [15] Upon annealing to 1100 K the sheet resistivity dropped further to 108
303 and 372 kWs q-1 for five four and three layers respectively This tunable electrical
conductivity of CNMs from an insulator to a conductor by annealing temperatures or
amounts of layers will be of value for CNMs to be utilized in micro- or nano-electronics
Figure 5 (A) RT sheet resistivity
of BPT multilayers as a function
of annealing temperature The er-
ror bars represent the standard de-
viation of measurements at differ-
ent spots on the samples (B) RT
linear currentndashvoltage curves for
2- 3- 4- and 5-layer samples
after annealing at 1100 K [15]
173
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
Figure 3 (A) XPS spectra of the C1 s and S2 p signals (a) Pristine biphenythiol
SAM (BPT) at room temperature (b) Cross-linked BPT (45 mCcm2) at RT (c)
Pristine BPT after annealing at 470 K (d) Cross-linked BPT after annealing at
470K (B) Temperature dependence of the C1 s signal of BPT as a function of
irradiation dose [14]
24 Electrical resistance
The performance of CNMs in electronic devices of course depends on their electrical
conductivity The sheet resistance of CNMs that have been annealed at temperatures be-
tween 800 K and 1200 K was determined by a two-point measurement in UHV scanning
tunneling microscopy (STM) and by four-point in ambient conditions CNMs suspended on
a gold grid were directly contacted by a STM tip in UHV The resistance was determined
from the current between the tip and the surrounding frame (Fig 4A) CNMs were also
transferred onto non-conductive silicon oxide and were then measured with four-probes
(Fig 4bB) [12] Figure 4C shows the sheet resistivity as a function of the annealing tem-
perature After annealing CNMs at ~800 K we find a sheet resistivity of ~10-8 kWsq-1 upon
rising the annealing temperature to ~1200 K this comes down to ~100 kWsq-1 The reason
for this unusual behavior is that upon annealing CNMs transform into graphene and thus
become conductive as will be described in more detail in section 27
172
Ai M and Golzhauser A
Figure 4 The resistivity of CNMs was determined by a two-point (STM) in UHV (A)
and four-point in ambient conditions (B) (C) The sheet resistivity corresponds to 10-8
kWsq-1 after annealing at 800 K Upon annealing to temperatures between 800 and
1200 K the currentvoltage curves are linear Increasing the annealing temperature to
1200 K the sheet resistivity drops to 100 kWsq-1 [12]
Multilayers of CNMs after annealing show more conductivity than a single layer of CNMs
as in Fig 5 [15] Upon annealing to 1100 K the sheet resistivity dropped further to 108
303 and 372 kWs q-1 for five four and three layers respectively This tunable electrical
conductivity of CNMs from an insulator to a conductor by annealing temperatures or
amounts of layers will be of value for CNMs to be utilized in micro- or nano-electronics
Figure 5 (A) RT sheet resistivity
of BPT multilayers as a function
of annealing temperature The er-
ror bars represent the standard de-
viation of measurements at differ-
ent spots on the samples (B) RT
linear currentndashvoltage curves for
2- 3- 4- and 5-layer samples
after annealing at 1100 K [15]
173
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
Figure 4 The resistivity of CNMs was determined by a two-point (STM) in UHV (A)
and four-point in ambient conditions (B) (C) The sheet resistivity corresponds to 10-8
kWsq-1 after annealing at 800 K Upon annealing to temperatures between 800 and
1200 K the currentvoltage curves are linear Increasing the annealing temperature to
1200 K the sheet resistivity drops to 100 kWsq-1 [12]
Multilayers of CNMs after annealing show more conductivity than a single layer of CNMs
as in Fig 5 [15] Upon annealing to 1100 K the sheet resistivity dropped further to 108
303 and 372 kWs q-1 for five four and three layers respectively This tunable electrical
conductivity of CNMs from an insulator to a conductor by annealing temperatures or
amounts of layers will be of value for CNMs to be utilized in micro- or nano-electronics
Figure 5 (A) RT sheet resistivity
of BPT multilayers as a function
of annealing temperature The er-
ror bars represent the standard de-
viation of measurements at differ-
ent spots on the samples (B) RT
linear currentndashvoltage curves for
2- 3- 4- and 5-layer samples
after annealing at 1100 K [15]
173
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
25 Elastic properties
The elasticity of CNMs was investigated by Zhang Beyer and Golzhauser [16] by using a
bulge test method in an AFM for the determination of the Youngrsquos modulus and other
quantities (Fig 6) Gas pressure was applied to one side of a CNM that was freely suspended
on a silicon substrate with a mm2 opening The pressure difference between the top and
bottom side of the membrane resulted in a CNM deflection that was recorded by line-
scanning the tip of an AFM (Fig 6A) or by monitoring the deflection of a fixed AFM tip
(central-point method Fig 6B) The central-point method has the advantage of reducing data
acquisition time and lowering the probability that the CNM ruptures during the experiment
Youngrsquos modulus and internal stress have been calculated from the obtained pressure-de-
flection relationship Maximum deflections several mm under at pressures up to 2 kPa were
measured The ultimate tensile strength reached 440 ndash 720 MPa with elongation to break at
values between 3 ndash 4 and the Youngrsquos modulus was obtained in the range of 6 to12 GPa
The Young modulus depends on the precursors of CNMs or the electron doses for the cross-
linking CNMs Below 20 mCcm2 no free-standing CNMs were formed whereas between
30 mCcm2 and 50 mCcm2 CNMs were formed With further irradiation the Youngrsquos
moduli remained constant even when the CNM was irradiated with much higher doses of
up to 80 mCcm2 This result was in accordance with the thermal stability experiments of
CNMs which indicated almost complete cross-linking at an electron dose of ~45 mCcm2
[16]
Figure 6 (A) (a) Schematic diagram of an AFM bulge test (b) CNM suspended over
an opening on Si substrate (c) AFM image of a non-pressurized CNM and a line
profile with a downward deformation of 200 nm (d) CNM under pressure of 750 Pa
with an upward 17 mm deflection (B) (a) Schematic of the central-point method (b)
Comparison of the line-scanning and the central-point method [16]
174
Ai M and Golzhauser A
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
26 Chemical modification of CNM surfaces
The chemical modification of CNMs primarily depends on the functionality of the precursor
molecules When CNMs made from 4rsquo-nitro-11rsquo-biphenyl-4-thiol molecules are electron
irradiated the hydrogen released during the cross-linking is reducing the terminal nitro
groups to amino groups These can be further functionalized with other molecules[17 18]
polymers [19 ndash 21] and proteins [22] as is shown in the schematic representation in Fig 7
Figure 7 Scheme of electron induced chemical lithography (A) 4rsquo-nitro-11rsquo-biphe-
nyl-4-thiol monolayer (B) An electron beam converts the terminal nitro groups of a
4rsquo-nitro-11rsquo-biphenyl-4-thiol monolayer to amino groups while the underlying aro-
matic layer is cross-linked (C) The cross-linked amino biphenyl thiol region is used
for the selective coupling of molecules R (small molecules or proteins or polymers)
An example are polymer brushes that can be grown onto CNMs by surface-initiated poly-
merization (SIP) [20 21] or self-initiated surface photopolymerization and photografting
(SIPGP) [22] In Fig 8 poly(4-vinyl pyridine) (P4VP) brushes were prepared on CNMs by
SIPGP In different solvents and depending on the pH values the morphology of the polymer
brushes changes In aqueous solution at pH = 7 the P4VP brushes are non-transparent on
glass slides (Fig 8B) This results from strong buckling due to collapsed polymer chains
with low solubility In ethanol or aqueous solutions at pH = 25 the P4VP brushes appear
transparent on glass and flat on gold substrate (Fig 8A and 8C) as ethanol is a very good
solvent for P4VP and at low pH values the polymers tend to dissolve in aqueous solution
due to the protonated pyridine group This visible response of the CNM bound polymer
brush to solvent stimulus may be useful for actuators sensors or displays providing
opportunities to adjust a surface to an environmental stimulus
Figure 8 Photographs (above) and AFM measurements (below) of P4VP carpets in
(A) ethanol (B) water at pH 7 and (C) water at pH 25 [22]
175
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
CNMs can also be decorated with distinct functional groups on both sides One side of the
CNM is occupied with the amino groups as aforementioned while the other bears sulfur
residues after separation from Au Both sides can react with other groups and lsquolsquoJanusrsquorsquo
CNMs that utilize this particularity have been constructed by Zheng et al [24] who
immobilized electron donors tetramethylrhodamine (TMR) to the top and electron acceptors
(ATTO647N) to the bottom side of the same CNM The synthesis processes are schemati-
cally displayed in Fig 9 Figure 10 shows fluorescence micrographs and SEM images of
CNMs functionalized on its amino side with TMR and on the thiol side with ATTO647N
The fluorescence resonance energy transfer (FRET) efficiency from the electron donor to the
electron acceptor through the short spacer (~1 nm thick CNM) was determined to be
effectively 100 while the distance is much shorter than the Forster radius This demon-
stration of lsquolsquoJanusrsquorsquo CNMs could lead to a platform for two-dimensional chemistry [24]
Figure 9 (A) A nanomembrane made from cross-linked biphenyl self-assembled
monolayers The 1 nm thick membrane has amino and thiol functional groups on its
upper and lower sides respectively (B) Functionalization with fluorescent dyes of the
upper and lower sides of the nanomembranes The amino side is functionalized with
TMR the thiol side with ATTO647N
176
Ai M and Golzhauser A
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
Figure 10 (A B) Fluorescence and (C) FRET images and (D) the corresponding
SEM image of a nanomembrane functionalized on its upper and lower sides with
TMR and ATTO647N respectively The FRET image has been recorded by exciting at
the donor wavelength and recording the fluorescence emission in the acceptor channel
All micrographs show the same area of the nanomembrane [23]
27 Transforming CNMs into graphene
CNMs transform into graphene when they are heated in ultrahigh vacuum to temperatures up
to 1200 K (pyrolysis) This has been demonstrated by Turchanin et al [12 15] by investi-
gating the pyrolyzed CNM with the help of Raman spectroscopy conductivity measure-
ments (also see 24) and transmission electron microscopy The Raman spectrum of un-
treated CNMs does not show any peaks between 1000 and 2000 cm-1 Upon annealing the
G-peak at 1605 cm-1 that is characteristic for graphene appears Parallel a rise of up to 5
orders of magnitude in the electrical conductivity is observed when the annealing tempera-
ture increases from room temperature to 1200 K see figure 4 This is due to the formation of
nanosized graphene crystallites in annealed CNMs Furthermore ordered domains com-
prised of individual atoms in annealed CNMs were observed by HRTEM (Fig 11) Utilizing
this bottom-up route from CNMs graphene can be manufactured with well-defined thick-
nesses and tunable electrical properties on various metal and insulator substrates This
unique resistance behavior allows to tune CNMs from insulator to conductor
177
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
Figure 11 (A-C) High-resolu-
tion transmission electron mi-
crograph (80 kV) of graphene
Tan = 1200 K fabricated from
CNMs The graphene sheet
was transferred onto a TEM
grid (A) Unprocessed image
(B and C) local Fourier trans-
forms from 36 3 nm2 areas in-
dicated by the arrows The pre-
sence of diffraction spots in pa-
nel (C) verifies the presence of
crystalline graphene areas in
panel (A) (D) Raman spectrum
(excitation wavelength 532
nm) of the same sample trans-
ferred to a SiO2Si surface
Opportunities for Nanotechnology
Interest in CNMs is motivated by their unique properties the tunable electrical conductivity
stiffness and surface chemistry A variety of applications for CNMs have been proposed and
here we discuss CNMs as nanotemplates nanopores and in biochips
Nanotemplates are low dimensional substrates having artificially or naturally patterned
structures They can be created by non-covalent interactions for example hydrogen bond-
ing metal-organic coordination and charge transfer van der Waals interactions [24] The
patterned structures can provide a controlled shape and composition nanotemplates have
attracted much interest in molecular engineering and recognition Patterned SAMs can be
simply fabricated by electron exposures [25] Such patterns which contain irradiated and
non-irradiated regions are useful templates for material deposition on the micro- and nanos-
cale
Nanopores have the ability to interact with atoms ions and molecules not only at the
surfaces but throughout the bulk They are broadly found in nature e g in zeolite minerals
or biomembranes In recent years artificial nanoporous materials were fabricated to be
178
Ai M and Golzhauser A
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
utilized for catalysis gas separation water purification and biomolecular separation [26]
Two-dimensional nanoporous materials i e sieves have a perspective in bioseparation or
proton-exchange in fuel cell when being integrated in microfluidic or membrane systems
Biochips as used in microfluidic or lsquolsquolab-on-chiprsquorsquo devices reduce laboratory procedures
and enable portable detection of agents In the past decades cell biotechnology for cell
culture and secretion [27] protein biochips [28] DNA biochips[29] have been a significant
expansion in research The key to the success of microfluidic-based biotechnology is to
immobilize biomolecules onto surfaces with high density For integration of 2D CNMs in
biochips the immobilization of biomaterials is indispensable Biomolecules such as proteins
and cells have been reported to be immobilized on the chemically tailored CNMs or
physically adsorbed on CNMs [10 30]
1 Micro- and nanotemplates
Micro- and nanotemplates can be used to fabricate metallic nanostructures on electrodes An
electrochemical surface template can be generated with structured SAMs The SAMs are
patterned by electron exposures through stencil masks with holes down to 1 mm and the
subsequent electrodeposition of copper on SAM patterned gold electrodes has been demon-
strated In non-irradiated biphenyl SAMs the copper peak in the cyclic voltammogram was
observed at 008 V from the CuSO4H2SO4 electrolyte solution For electron irradiated
SAMs the deposition peak was shifted to more negative potentials (DE = 015 V) The
electrodeposition of copper nanostructures was thus selectively generated on SAM templates
at a deposition potential of +005V where the irradiated biphenyl perfectly inhibited the
copper deposition as shown in Fig 12 [31 32]
Figure 12 (A) Schematic illustration of the electrochemical behavior of a BP12 SAM
For the native film copper deposition is expected to be defect mediated (1) Electron
irradiation links the biphenyl moieties which can then mask intrinsic defects (2) or
radiation induced damage in the alkane spacer (3) (B) SEM-micrograph of Cu struc-
tures deposited on a BPT SAM template patterned by proximity printing (300 eV
64000mCcm2) Deposition parameters 10 mM CuSO4 +005 V (vs NHE) 120 s
[31 32]
179
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
2 Micro- and nanopores
To drill holes in a 1-nm-thick film CNMs fast and low-cost methods were demonstrated
Photolithography can be used to define the size and shape of pores that are then etched away
by UVozone cf Fig 13 [33] In a more advanced method periodic nanopores are fabricated
by extreme UV interference lithography (Fig 14) The size of the nanopores can be flexibly
tuned by choosing proper EUV masks with a lower limit of currently ~20 nm [34]
Figure 13 (A) (a) A SAM of BPT is exposed to UVozone through a mask (b) The
damagedoxidized SAM in the exposed regions is rinsed away and (c) exposed to
electrons (d) The remaining SAM is cross-linked (B) (a) SEM image of a BPT SAM
after UVozone patterning through a TEM grid with 3 mm circular holes (b) SEM
after cross-linking (a) with an electron dose of 50 mCcm2 (c) LFM of a UVozone
patterned BPT-SAM (d) LFM of (c) after cross-linking [33]
Figure 14 (A) Fabrication scheme of nanosieve membranes (a) A SAM of NBPT is
formed on a gold substrate b) Generation of amino-terminated crosslinked areas
(nanosheets) in the SAM via EUV-IL c) Spin-coating of a polymer film and peeling
off from the gold substrate d) Transfer of the nanosheet with the hardened
polymer e) Formation of a 1-nm-thin freestanding nanosieve by dissolving the
polymer on a new holey substrate
180
Ai M and Golzhauser A
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
(B) TEM characterization of nanosieve membranes Dark-field mode images of
~1-nm-thin nanosieves with a) 138 plusmn 17-nm holes (interference grating periodicities
of 2256 200 nm2 irradiation dose of 70 J cm-2) b) 100 plusmn 15-nm holes (interference
grating periodicities of 2256 200 nm2 irradiation dose of 120 J cm-2) and c)
31 plusmn 6-nm holes (interference grating periodicities of 1006 90 nm2 irradiation dose
of 50 J cm-2) [34]
3 Biochips
31 Chemically tailored CNMs
To demonstrate CNMs as protein chips Turchanin Tinazli and co-workers used the barrel-
shaped 20S proteasome complex from the archaea Thermoplasma acidophilum as a biological
model system periodically binding on CNMs [22] The macromolecular proteins were engi-
neered on CNMs via complexation between histidine-tagged proteins and transition metal ions
Ni (II) The Nickel-nitrotriacetic acid (NTA) and histidine-tagged chelator system is a powerful
and universal tool for the one-step isolation and purification of gene products [35] For the
application in protein arrays and biosensors long-term stability is required to overcome the
limitation of metal leaching and rapid protein dissociation [36] Therefore the authors intro-
duced cumulated NTA clusters on CNMs with multivalent interaction sites to load and regen-
erate His6-tags proteins This concept of periodically binding proteins on CNMs shed light on
immobilizing and then detecting single proteins as a biochip as shown in Fig 15
Figure 15 (A) Schematic representation of the protein chip assembly (indashv) Con-
trolled immobilization of His-tagged protein complexes (here proteasome) in end-on
orientation (vi) b) Protein repellent EG3-OH matrix thiols c) Multivalent tris-NTA
chelator with protected carboxyl functionality (B) Controlled immobilization of dif-
ferent proteins on the chip surface a b) Confocal laser scanning microscopy images
of specifically immobilized Atto565-labeled maltose-binding proteins (His10-MBP)
c) Topographic AFM image of the same chip after the regeneration with imidazole d)
In situ AFM scan of a microarray of immobilized His6-proteasome complexes e) The
same surface after regeneration AFM images are 146 14 mm2 the z-scale corre-
sponds to 20 nm [22]
181
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
32 Physically immobilized on CNMs
Non-covalent interaction (van der Waals and electrostatic forces) between biomolecules and
CNMs provides an alternative and simple way to investigate the biocompatibility of CNMs
Rhinow et al have prepared purple membranes (PMs) from Halobacterium salinarum a
2-D crystalline monolayer of bacteriorhodopsin and lipids as a test specimen on CNMs [37]
Characterization of PM on CNMs by cryogenic high-resolution transmission electron micro-
scopy (cryo-EM) (Fig 16 B) reveals that trehalose embedded PM samples have been imaged
on CNMs and the amplitudes as well as phases can be recovered up to high resolution
ranges The biocompatibility of CNMs to PMs is further confirmed with tapping-mode AFM
in a buffer solution The 2D crystal lattice of PMs on CNMs was visualized and the force
spectroscopy obtained by AFM exhibited non-folding peaks due to the extracellular side of
PMrsquos physical adsorption on CNMs [37]
Figure 16 (A) Schematic representation of PMs on CNMs (A) PMs on freestanding
CNMs PMs and CNMs are drawn on scale with respect to their thickness (B) (1)
PMs sticking to freestanding CNMs (2) PMs supported by CNMs plus thick carbon
support and (3) holey carbon without CNMs (C) PMs on silicon-supported CNMs
(B) (A) TEM image of trehalose-embedded PMs on CNMs at room temperature A
holey carbon film supports the CNM (B) Enlarged view of the central area of (A) (red
square) (C) FFT of area 1 of (D) Thon rings are visible due to phase contrast of the
thick holey carbon support (D) TEM image of a sample-free CNM area which spans
two adjacent holes (E) FFT of free-hanging CNM (area 2 of (D)) Thon rings are
absent (F) Fourier transform of an image of a single trehalose-embedded PM on
cCNM at liquid nitrogen temperature White arrows indicate the unit cell vectors
corresponding to the 624 A lattice The red arrowhead points to the (4 3) reflection
at 89 A resolution (G) A projection map of PMs on CNMs at 4 A resolution as
calculated from eight averaged images in a defocus range of 500 ndash 1000 nm [37]
182
Ai M and Golzhauser A
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
Conclusions and Outlook
This article provides an overview on recent trends in CNM research The fabrication of
CNMs from various self-assembled small aromatic molecules of a variety of substrates has
been reviewed The exploration of the properties of these two-dimensional films was revis-
ited among them the tuning of its chemical mechanical and electronic function and its
conversion to graphene after pyrolysis Janus CNM in which the top of the CNM is
decorated with electron donors and while its bottom with electron acceptors and their used
as lsquolsquorulersrsquorsquo to determine the length (generally 1 nm ~ 8 nm) of a molecular spacer between
donor and acceptor incorporated by biomolecules is discussed When both sides of the CNM
are decorated with site-specific biomolecules CNMs can be utilized to mimic biological
membranes There is a range of further applications in nanoscience and nanotechnology for
instance micro- or nanotemplates micro- or nanopores and biochips The tunable conduc-
tivity and surface chemistry will permit CNMs to be integrated in lab-on-a-chip devices for
liquid or gas separation electronics MEMSNEMS devices in the near future Opportunities
and challenges co-exist for example in developing new routes for preparing CNMs of
macroscopic size and understanding the detailed nanostructures of CNMs These unsolved
fundamental questions together with potential applications will provide compelling motiva-
tion for CNM research in the coming years
Acknowledgements
The described work was made possible by financial support from the Volkswagenstiftung
the Deutsche Forschungsgemeinschaft and the German Bundesministerium fur Bildung und
Forschung (BMBF)
References
[1] Huang G Mei Y (2012) Adv Mater 242517 ndash 2546
httpdxdoiorg101002adma 201200574
[2] Decher G (1997) Science 2771232 ndash 1237
httpdxdoiorg101126science27753301232
[3] Vendamme R Onoue S-Y Nakao A Kunitake T (2006) Nature Materials
5494 ndash 501
httpdxdoiorg101038nmat1655
[4] Louie J S Pinnau I Reinhard M (2008) J Membr Sci 325793 ndash 800
httpdxdoiorg101016jmemsci200809006
[5] Nardin C Winterhalter M Meier W (2000) Langmuir 167708 ndash 7712
httpdxdoiorg101021la000204t
183
1 nm Thick Functional Carbon Nanomembrane (CNM) New Opportunities for Nanotechnology
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
[6] Li X Cai W An J (2009) Science 3241312 ndash 1314
httpdxdoiorg101126science1171245
[7] Novoselov K S Geim A K Morozov S V Jiang D Zhang Y Dubonos S V
Grigorieva I V Firsov A A (2004) Science 306666 ndash 669
httpdxdoiorg101126science1102896
[8] Chhowalla M Shin H S Eda G Li L-J Loh K P Zhang H (2013) Nature
Chemistry 5263 ndash 275
httpdxdoiorg101038NCHEM 1589
[9] Eck W Kuller A Grunze M Volkel B Golzhauser A (2005) Adv Mater
172583 ndash 2587
httpdxdoiorg101002adma200500900
[10] Turchanin A Schnietz M El-Desawy M Solak H H David C Golzhauser A
(2007) Small 32114 ndash 2119
httpdxdoiorg101002smll200700516
[11] Turchanin A Kafer D El-Desawy M Woll Ch Witte G Golzhauser A (2009)
Langmuir 257342 ndash 7352
httpdxdoiorg101021la803538z
[12] Turchanin A Beyer A Nottbohm C T Zhang X Stosch R Sologubenko A
Mayer J Hinze P Weimann T Golzhauser A (2009) Adv Mater 211233 ndash
1237
httpdxdoiorg101002adma200803078
[13] Golzhauser A Woll Ch (2010) ChemPhysChem 113201 ndash 3213
httpdxdoiorg101002cphc201000488
[14] Turchanin A El-Desawy M Golzhauser A (2007) Appl Phy Lett 90053102
httpdxdoiorg10106312437091
[15] Nottbohm C T Turchanin A Beyer A Stosch R Golzhauser A (2011) Small
7874 ndash 883
httpdxdoiorg101002smll201001993
[16] Zhang X Beyer A Golzhauser A (2011) Beilstein J Nanotechnol 2826 ndash 833
httpdxdoiorg103762bjnano292
[17] Golzhauser A Eck W Geyer W Stadler V Weimann T Hinze P Grunze M
(2001) Adv Mater 13806 ndash 809
httpdxdoiorg1010021521-4095(200106)13113C803AID-ADMA8063E30CO2-W
184
Ai M and Golzhauser A
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
[18] Nottbohm C T Sopher R Heilemann M Sauer M Golzhauser A (2010) J Bio
Tec 149267 ndash 271
httpdxdoiorg101016jjbiotec201001018
[19] Schmelmer U Jordan R Geyer W Eck W Golzhauser A Grunze M
Ulman A (2003) Angew Chem Int Ed 42559 ndash 563
httpdxdoiorg101002anie200390161
[20] Schmelmer U Paul A Kuller A Steenackers M Ulman A Grunze M
Golzhauser A Jordan R (2007) Small 3459 ndash 465
httpdxdoiorg101002smll200600528
[21] Amin I Steenackers M Zhang N Beyer A Zhang X Pirzer T Hugel T
Jordan R Golzhauser A (2010) Small 61623 ndash 1630
httpdxdoiorg101002smll201000448
[22] Turchanin A Tinazli A El-Desawy M Groszligmann H Schnietz M Solak H
H Tampe R Golzhauser A (2008) Adv Mater 20471 ndash 477
httpdxdoiorg101002adma200702189
[23] Zheng Z Nottbohm C T Turchanin A Muzik H Beyer A Heilemann M
Sauer M Golzhauser A (2010) Angew Chem Int Ed 498493 ndash 8497
httpdxdoiorg101002anie201004053
[24] Cicoira F Santato C Rosei F (2008) Top Curr Chem 285203 ndash 267
httpdxdoiorg101007128_2008_2gt101007128_2008_2
[25] Golzhauser A Geyer W Stadler V Eck W Grunze M Edinger K
Weimann T Hinze P (2000) J Vac Sci Technol B 183414 ndash 3418
httpdxdoiorg10111611319711
[26] Davis M E (2002) Nature 417813 ndash 821
httpdxdoiorg101038nature00785
[27] Yang M Yao J Duan Y (2013) Analyst 13872 ndash 86
httpdxdoiorg101039c2an35744e
[28] Rusmini F Zhong Z Feijen J (2007) Biomacromolecules 81775 ndash 1789
httpdxdoiorg101021bm061197b
[29] Dutse S W Yusof N A (2011) Sensors 115754 ndash 5768
httpdxdoiorg103390s110605754
[30] Biebricher A Paul A Tinnefeld P Golzhauser A Sauer M (2004) Journal of
Biotechnology 11297 ndash 107
httpdxdoiorg101016jjbiotec200403019
185
Organic Charge Transfer Systems the Next Step in Molecular Electronics
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M
[31] Kaltenpoth G Volkel B Nottbohm CT Golzhauser A Buck M (2002) J Vac
Sci Techno B 202734 ndash 2738
httpdxdoiorg10111611523026
[32] Volkel B Kaltenpoth G Handrea M Sahre M Nottbohm C T Kuller A
Paul A Kautek W Eck W Golzhauser A (2005) Surface Science 59732 ndash 41
httpdxdoiorg101016jsusc200408046
[33] Nottbohm CT Wiegmann S Beyer A Golzhauser A (2010) Phys Chem Chem
Phys 124324 ndash 4328
httpdxdoiorg101039B923863H
[34] Schnietz M Turchanin A Nottbohm C T Beyer A Solak H H Hinze P T
Weimann Golzhauser A (2009) Small 52651 ndash 2655
httpdxdoiorg101002smll200901283
[35] Hochuli E Bannwarth W Dobeli H Gentz R amp Stuber D (1988) Bio-
Techniques 61321 ndash 1325
httpdxdoiorg101038nbt1188-1321
[36] Nieba L NiebaAxamnn S E Persson A Hamalainen M Edebratt F
Hansson A Lidholm J Magnusson K Karlsson A F Pluckthun A (1997)
Anal Biochem 252217 ndash 228
httpdxdoiorg101006abio19972326
[37] Rhinow D Vonck J Schranz M Beyer A Golzhauser A Hampp N (2010)
Phys Chem Chem Phys124345 ndash 4350
httpdxdoiorg101039b923756a
186
Huth M